test 7

Question 1

Three renal processes

Answer 1

 Glomerular filtration
 Tubular reabsorption
 Tubular secretion

Question 2

Excretion =

Answer 2

Filtration – Reabsorption +

Secretion

Question 3

Filtration only

Answer 3

 Excretion = Filtration

 Waste products (creatinine)

Question 4

Filtration and partial reabsorption

Answer 4

 Excretion = Filtration – Reabsorption

 Electrolytes (sodium, chloride)

Question 5

Filtration and complete reabsorption

Answer 5

 Nothing excreted

 Nutritional substances (amino acids, glucose)

Question 6

Filtration and secretion

Answer 6

 Excretion = Filtration + Secretion (no reabsorption)

 Organic acids & bases

Question 7

Excretion Rate

Answer 7

 Filtration, reabsorption, & secretion closely regulated based on needs of the body
 Increased sodium -> increased filtration -> decreased reabsorption = increased excretion
 Most substances see a high filtration AND a high reabsorption rate
 Small changes in filtration and/or reabsorption will produced significant changes in excretion rate

Question 8

Why High Filtration Rate??

Answer 8

 Allows rapid removal of waste products
 These substances depend on filtration for adequate removal (i.e. not reabsorbed or secreted)
 Allows multiple passes of the blood volume through the kidneys each day
 GFR = 180 L/day versus 3 to 4 liters of plasma volume
 Allows complete filtering of plasma volume 60 times each day
 Allows rapid and precise control of body fluid volume and composition

Question 9

Renal blood flow (RBF) amount

Answer 9

22% of total cardiac output

Question 10

Glomerular Filtration Rate (GFR) amount

Answer 10

180 Liters/day OR 125 mls/minute

Question 11

Filtration Fraction =

Answer 11

GFR / Renal Plasma Flow

Question 12

Each minute how much of the plasma flowing through the kidneys is filtered (i.e. enters renal tubules)?

Answer 12

20% of the plasma

Question 13

percentage of plasma in the blood

Answer 13

RBF x (1 - HCT) = Renal Plasma Flow

Question 14

If GFR goes up with no change in plasma flow

Answer 14

Filtration fraction is going up

Question 15

Normal reabsorption ≈

Answer 15

178.5 Liters/day (124 mls/minute)

Question 16

Normal urine output ≈ (L/day)

Answer 16

180 – 178.5 ≈ 1.5 Liters/day

Question 17

Normal urine output ≈ (mls/min)

Answer 17

125 -124 ≈ 1 mls/minute

Question 18

Small Change in GFR Could Produce Large Change in what?

Answer 18

Urine output

 10% increase in GFR would produce a 13-fold increase in urine output

Question 19

Three major layers (not 2) of the Glomerular Capillary

Membrane

Answer 19

 Endothelial cell layer
 Basement membrane layer
 Epithelial cell layer

Question 20

Glomerular Capillary Membrane

Answer 20

 Filters significantly more volume than normal capillaries – Thicker but more porous
 Endothelial layer perforated by thousands of fenestrations (small holes)
 Protein passage prevented by negative charge on surface of endothelial cells
 Basement membrane allows movement of water and small solutes
 Protein passage prevented by proteoglycan mesh and negative charge
 Epithelial layer not continuous
 Slit pores present between adjacent podocytes – allow free movement of water and small solutes
 Negative charge of surrounding epithelial cells hinders protein filtration
 Overall pore size approximately 8 nanometers (80 angstroms)

Question 21

Filterability of Solute

Answer 21

 Filterability of 1.0 means freely filtered (at the same rate as water)
 Concentration in filtrate = plasma concentration
 Filterability of 0.75 means filtered 75% as quickly as water (more water than solute is filtered
 Filtrate concentration < plasma concentration
 Albumin smaller than pore size (6 nm vs. 8 nm) but negative charge prevents passage

Question 22

Myoglobin (not usually found in blood) filterability

if plasma concentration was 54 ug/dL, what is the glomerular filtrate

Answer 22

filterabilty = .75
54(.75)= 40.5 ug/dL
-more water filtered at a faster rate

Question 23

Albumin filterability if plasma concentration was 5 gm/dL, what is the glomerular filtrate

Answer 23

filterability = .005
5(.005) = .025 gm/dL

Question 24

Filterability – Effect of Charge

Answer 24

-positively charged ions will be favorably filtered
-a negative charge filterability decreases significantly
 In some renal diseases, the negative charge of basement membrane is lost before any histological changes are seen – appearance of albumin
in urine is an early indicator

Question 25

Glomerular Filtration Rate

Answer 25

 GFR = Kf x Net filtration pressure  Kf is the glomerular capillary filtration coefficient - GFR = filtration fraction x renal plasma flow -blood flow through kindeys goes up, GFR goes up

Question 26

Net filtration pressure

Answer 26

≈ 10 mmHg  Promotes filtration  Glomerular hydrostatic pressure (60 mmHg)  Bowman’s capsule oncotic pressure (0 mmHg) (factor with disease)  Inhibits filtration  Glomerular oncotic pressure (32 mmHg)  Bowman’s capsule hydrostatic pressure (18 mmHg)

Question 27

Glomerular Capillary Filtration Coefficient

Answer 27

 Affected by overall hydraulic conductivity and surface area of the glomerular capillaries  Not able to measure directly  Kf = GFR / Net filtration pressure  Kf = 125 mls/min / 10 mmHg = 12.5 mls/min/mmHg

Question 28

Normal Kf for glomerular capillaries vs other capillaries

Answer 28

 Kf = 4.2 mls/min/mmHg/100 grams of tissue for glomerular cap  Normal Kf other capillaries = 0.01 mls/min/mmHg/100 gm

Question 29

Filtration Coefficient and GFR

Answer 29

 Filtration fraction = GFR / RPF  Direct positive relationship  Usually not part of day-to-day control of GFR  Can be affected by disease  Decreasing number of functional glomerular capillaries (decreased surface area)  Increasing thickness of membrane (decreased hydraulic conductivity)  Hypertension & diabetes mellitus  A decrease in RBF (no initial change in GFR) will increase the filtration fraction thus producing a decrease in GFR

Question 30

Oncotic Pressure – Glomerulus

Answer 30

 Increased glomerular oncotic pressure = Decreased GFR  Decreased glomerular oncotic pressure = Increased GFR  As blood passes through glomerulus plasma oncotic pressure will increase ≈ 20%  Approximately 20% of fluid is filtered producing increased [protein]  Plasma oncotic pressure ≈ 28 mmHg entering glomerulus  Glomerular oncotic pressure ≈ 36 mmHg as blood leaves glomerulus  [32 mmHg average]

Question 31

Factors Affecting Glomerular Oncotic Pressure

Answer 31

 Plasma protein concentration of arterial blood  Increased plasma protein concentration will increase glomerular oncotic pressure which will decrease GFR  Fraction of plasma being filtered (filtration fraction)  Increased filtration fraction means more plasma is being filtered from each ml of blood in the glomerulus  As blood is concentrated the oncotic pressure of blood remaining in the glomerulus increases which will decrease GFR

Question 32

Changing RBF with constant glomerular hydrostatic pressure thus has an effect on GFR

Answer 32

 Increased RBF – Decreased Fraction – Decreased glomerular oncotic pressure – Increased GFR

Question 33

if filtration fraction goes down across the whole capillary

Answer 33

-protein concentration has changed -filtering less holding onto less fluid so GFR increases

Question 34

The higher the filtration fraction across the capillary

Answer 34

- the lower the GFR will be

Question 35

Hydrostatic Pressure - Glomerulus

Answer 35

 Increased pressure = Increased GFR |  Decreased pressure = Decreased GFR

Question 36

How can you change your golomerular hydrostatic pressure

Answer 36

 Arterial pressure  Increased MAP = Increased GFR [Buffered by autoregulation of flow to keep consistent glomerular pressure]  Afferent arteriole resistance  Efferent arteriole resistance

Question 37

Afferent Arteriole Resistance

Answer 37

 Increased constriction = Decreased glomerular hydrostatic pressure = Decreased GFR  Decreased constriction = Increased glomerular hydrostatic pressure = Increased GFR  As constriction increases, RBF also decreases.  But GFR decreases at a faster rate -3 times the resistance glomerular filtration rate is 0 ml/min because net filtration force is 0 -don't need complete stasis to stop golmerular filtration rate

Question 38

Efferent Arteriole Resistance intially

Answer 38

 Increased constriction = Increased pressure = Increased GFR  Decreased constriction = Decreased pressure = Decreased GFR

Question 39

Efferent Arteriole Resistance whole process

Answer 39

 As constriction increases, RBF will decrease while glomerular pressure increases  INITIALLY the change in glomerular pressure has more effect than the decrease in RBF which produces an overall increase in GFR.  [Increase in glomerular pressure greater than decrease in RBF] -BUT as constriction continues to increase the change in filtration fraction begins to play a role:  Filtration fraction increases (decreased blood flow, increased GFR) which results in higher glomerular colloid oncotic pressure which decreases GFR  When effect of the increase in glomerular oncotic pressure exceeds the effect of the increase in hydrostatic pressure, the GFR will decrease

Question 40

Hydrostatic Pressure – Bowman’s Capsule

Answer 40

 Increased hydrostatic pressure = Decreased GFR  Decreased hydrostatic pressure = Increase GFR  Normally does not play a primary role in controlling GFR  Obstruction of urinary tract (kidney stone)  Could produce big increase in pressure with big decrease in GFR